Common element combinations

Always include heat-cfntools in images that you intend to boot via heat : if
that is not done, then the user ssh keys are not reliably pulled down from the
metadata server due to interactions with cloud-init.

Architecture

OpenStack images are intended to be deployed and maintained using Nova + Heat.

As such they should strive to be stateless, maintained entirely via automation.

Configuration

In a running OpenStack there are several categories of config.

per user - e.g. ssh key registration with nova: we repeat this sort
of config every time we add a user.

inter-node - e.g. credentials on rabbitmq for a given nova compute node

application state - e.g. ‘neutron net-create …’ : settings that
apply to the whole cluster not on a per-user / per-tenant basis

We have five places we can do configuration in TripleO:

image build time

in-instance heat-driven (ORC scripts)

from outside via APIs

orchestrated by Heat

Our current heuristic for deciding where to do any particular configuration
step:

per user config should be done from the outside via APIs, even for
users like ‘admin’ that we know we’ll have. Note that service accounts
are different - they are a form of inter-node configuration.

local node configuration should be done via ORC driven by Heat and/or
configuration management system metadata.

inter-node configuration should be done by working through Heat. For
instance, creating a rabbit account for a nova compute node is something
that Heat should arrange, though the act of creating is probably done by a
script on the rabbit server - triggered by Heat - and applying the config is
done on the compute node by the local node script - again triggered by Heat.

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